This is a new application that brings together expertise in radiation biology and robotic high throughput drug screen technology to identify new radiation sensitizers and protectors for use in clinical radiation oncology and in the event of radiological terrorism. Three specific aims are proposed. Specific Aim 1 will implement a high throughput cell-based screen to identify compounds that can sensitize/protect human cells to/from ionizing radiation. This is a drug discovery aim that will allow us to identify lead molecules that are radio-sensitizers or radio-protectors from a library consisting of ~40,000 compounds. Specific Aim 2 will validate the results obtained in Aim 1 using clonogenic cell survival assays. Different drug concentrations and exposure times will be investigated at increasing radiation doses. Aim 2 will also test the hypothesis that radiation protectors are effective when used after irradiation. Once we have confirmed the initial observations regarding sensitization or protection, we will use isogenic cells that lack one or both alleles of genes known to be disrupted in tumor cells to determine whether lead compounds sensitize/protect differentially in wild type cells versus cells with well characterized mutations commonly found in cancer. Specifically we will test the hypothesis that compounds will differentially sensitize/protect wild type cells compared with cells containing genetic alterations commonly found in cancer cells. Specific Aim 3 will test the hypothesis that the sensitizers/protectors identified in Aim 1 and confirmed in Aim 2 will not predispose surviving cells to enhanced genomic instability. Exposure to clinically relevant doses of radiation in the presence of sensitizers or protectors will not kill all cells. Using a green fluorescence protein-based reporter assay we will test the hypothesis that the progeny of cells surviving irradiation +/-sensitizer or protector are not more likely to manifest genomic instability as measured by delayed mutation and hyperrecombination. Using a micronucleus assay we will test the hypothesis that the progeny cells surviving irradiation +/- sensitizer or protector are not more likely to manifest genomic instability as measured by delayed chromosomal instability. All technology and cell lines are available and in place at the University of Maryland. We have the expertise to identify new radiation sensitizers/protectors for use in the clinic and in the event of radiological terrorism. Successfully achieving the proposed research goals will be a significant contribution to patients undergoing radiation therapy and to the public in the event of terrorism involving radioactive material. PUBLIC HEALTH RELEVENCE: There are two feasible and potentially very significant goals to this application. The first is to use state of the art technologies to identify compounds that can sensitize cancer cells to radiation- induced cell killing and thus improve radiation therapy. The second is to use those same technologies to find unique compounds that can protect against deleterious radiation effects and thus protect individuals in the event of a radiological incident.